Most cameras are provided with one or more mechanical systems which, during the sequence of taking a picture, are displaced from one end position to another, and thereafter returned to the first end position in readiness for the taking of a subsequent picture. Such systems include, for example, the viewing mirror mechanism of a single lens reflex camera, and/or the shutter mechanism and/or the diaphragm mechanism.
In terms of the viewing mirror mechanism, a common displacement means includes a return setting member, a mirror-up spring and an associated return spring, a latch and a mirror-up mechanism. A shutter charging operation energizes both the mirror-up spring and the return spring while bringing the return setting member to its set position where it is locked by the latch. A shutter release causes the mirror-up member to be initially actuated under the influence of the mirror-up spring to drive the mirror upward. Immediately after termination of shutter operation the return setting member is unlocked from the latch, thereby allowing the setting member to be returned under the influence of the return spring until the mirror returns to its original position.
The above-described mechanism suffers from many disadvantages. Firstly, to guarantee that the mirror will indeed reach its end positions, even if the camera in which it is fitted is operated in an inverted state, the two springs must be sufficiently tensioned to overcome mechanical losses so that the mirror arrives at the end positions with at least some tension remaining in the springs. This implies that the mirror is accelerated during its entire movement and therefore reaches its end positions at a maximum velocity for that movement. At the end positions the kinetic energy of the mirror and driving mechanism must be absorbed and, due to the relatively high velocity, the deceleration forces can be sufficiently high to cause shake of the camera, thereby giving rise to a blurred picture. The high velocity of the mirror also imposes problems with latching of the mirror at its end positions since the mirror can bounce back before the latch engages. The requisite high deceleration forces lead to increased noise levels and vibration whilst decreasing the life-span of the camera.
Many partial solutions to the above-described problem have been proposed. For example, in U.S. Pat. No. 4,192,598 a damping mechanism for reducing noise and shock is provided either on an element moving integrally with the mirror or on the driving lever. In U.S. Pat. No. 4,385,820 the mirror is raised and lowered by means of a gear train, one gear of which engages a sector-shaped gear integral with a mirror supporting member. Due to the weight of the mirror, large inertial forces have to be overcome and thus a greater driving force is necessary. In order to avoid bounce of the mirror at its end positions, U.S. Pat. No. 4,385,820 proposes a mechanical brake system for applying a braking force to the gear mechanism during the latter stages of the mirror's movement.
Whilst the systems described above may reduce the levels of noise and vibration, they also add to the complexity of the camera and occupy valuable space. In addition, the energy consumption of such systems is relatively high since, on the one hand, the relatively strong springs must be reenergized after each sequence and, on the other hand, not all of the energy in the springs is utilized.
A recent development in the field of mirror mechanisms makes use of a link mechanism driven by an electro-mechanical transducer, normally a d.c. motor. When a picture is to be taken, the motor is activated and the mirror is driven up to its end position. Thereafter the mirror is returned to its lower position by driving the motor with reversed polarity. In its simplest form even this type of mechanism needs some kind of braking or damping to avoid bounce. One possible, though not yet practicable, alternative could be to introduce intelligent control of the motor's torque to thereby control the acceleration and velocity of the mirror according to predetermined patterns. This alternative does however require advanced and fast-acting electronics, together with a quantity of cabling, sensors, printed circuit space, etc.
Another proposed solution is to use a first pre-energized spring to drive the mirror mechanism from its first end position towards the other end position. At the end of the movement the mirror mechanism is braked by a second spring. The energy from the braking is stored in the second spring and is used to accelerate the mirror mechanism during the beginning of its return movement. At the end of the return movement the mirror mechanism is braked by the first spring. This braking operation returns the first spring to the pre-energized state. An example of such a mirror mechanism is disclosed in U.S. Pat. No. 4,091,399. The mechanism can also be used for camera shutters, see U.S. Pat. Nos. 3,470,808 and 2,980,004.
However, in order to operate satisfactorily, these mechanisms require additional energy to overcome, for example, frictional losses. In the mechanisms referred to, the additional energy is supplied before the start of the movement. To guarantee that all mirror mechanisms will reach their end positions under all possible conditions, the amount of additional energy has to be set according to a "worst-case". This results in a waste of energy which is a disadvantage in camera systems with limited power resources.
As a new cycle of movement can not start until the additional energy has been supplied, the time required for the supply will severely limit the repetition frequency of the cycle of movement.
Another disadvantage of the proposed solution is that as the additional energy is constant, resulting in a variable operational time for the movement due to frictional variations, spring properties etc.
In terms of camera shutters, two main types are used, i.e. central (or sector) shutters and focal plane shutters. Focal plane shutters include both blade shutters and curtain shutters. These may be either spring-driven or motor driven. As with mirror mechanisms, a major problem lies with the adequate absorption of the kinetic energy of the shutter mechanism when approaching its end positions. Several partial solutions to this problem are proposed in the art, such as in GB-A-2 065 315, U.S. Pat. Nos. 4,829,329, 4,480,900 and 5,060,000, though all add to the complexity of the camera.